The present invention relates, in general, to methods of repairing asphaltic roads, airport runways and the like and, more specifically, to methods for repairing deep, thermal cracks and/or cold joints in asphaltic roads, airport runways and the like.
Description of the Art
Asphaltic roads including asphalt airport runways have a tendency over time to crack due to weathering and internal stresses of the asphaltic material. In the past, when a crack has occurred in the surface of a road or runway, a thermoplastic sealant would be inserted into the crack to attempt to seal the crack. The difficulty with this technique is that the thermoplastic material that is inserted into the crack has a tendency itself to become less thermoplastic and to shrivel or shrink thereby exposing the interior of the crack. Once this has occurred, the weathering that would normally occur and the freezing and thawing of the asphaltic surface and roadway would further deteriorate the asphalt surrounding the crack. Such deterioration would decrease the useful life of the roadway.
A method of reconstructing asphalt pavement as disclosed in U.S. Pat. No. 3,970,404 which uses a series of heat application steps to soak heat into the top layer of the asphaltic surface to a predetermined depth of approximately one inch. The softened asphalt is then scarified and subsequently compacted or leveled into a new trafficable surface. A radiant heater is used to provide suitable amounts of heat to soften the asphalt. This patent discloses the generally known heating characteristic of asphaltic roadways where the surface of the asphalt pavement should be heated to a temperature within the range of 225.degree. F. to about 325.degree. F. This is due to the fact that asphalt deteriorates at temperatures above 350.degree. F. As a result, only the top one to one and a quarter inches of the asphalt roadway are heated and softened by this technique thereby permitting only repair of the top one to one and a quarter inch of asphalt roadway.
U.S. Pat. No. 4,084,915 discloses a similar method for reconditioning and resurfacing pavement in which a bituminous liquid or rejuvenating agent is sprayed over the area to be repaired. An infrared heater is passed over the pavement heating the bituminous liquid and the top surface of the asphalt to a temperature of approximately 225.degree. F. to soften the upper surface of the pavement. Mechanical choppers are then used to break up the softened pavement down to a depth of approximately one inch. Power operated mechanical mixers are then employed to mix and fully integrate the disintegrated bituminous concrete or asphalt with the bituminous liquid. Once this is done, a screed is passed over the asphalt to level the surface of the roadway. This method is suited for resurfacing large areas of asphalt roadway down to a depth of approximately one inch.
U.S. Pat. No. 1,230,894 discloses another method of repairing asphalt pavements in which a flammable solvent is impregnated in the area surrounding a crack in an asphalt surface. The solvent is ignited to soften the asphalt and to form a flux with new material which is added to the crack and the top layer of asphalt. However, only the top layer of asphalt can be impregnated with the flammable solvent such that only asphalt down to a depth of approximately one inch will be softened by the igniting of the flammable solvent. Further, the use of such flammable solvents is known to deteriorate the characteristics of asphalt since the temperature of the asphalt is raised above 350.degree. F.
The above-described methods of repairing cracks in asphaltic pavement or roadway are usable with small depth cracks extending down to one and one and a quarter inches since this is the maximum possible depth of asphalt which can be heated to a softened state at a temperature of 325.degree. F. to 350.degree. F. Such methods are totally ineffective in repairing full depth cracks extending the full or substantially through the six to eight inch depth of a standard asphalt pavement layer down to the underlying bedrock or ground. Such cracks are known as "thermal cracks" which are caused by the expansion and contraction of the pavement and the ground underneath it. Such full depth cracks can also include a crack caused by a cold joint. This type of crack occurs where the asphalt previously installed by the paver in 12 foot widths is cool when the adjacent 12 foot width is added. This places the hot asphalt edge against a cold asphalt edge creating a "cold joint". Such joints can be as wide as a thermal crack and can run from one half inch to six inches in width as well as extending the full six to eight inch depth of the asphalt pavement.
The above-described methods of repairing cracks in asphalt pavement are not effective in repairing full depth thermal cracks or cold joints extending a considerable distance through the asphalt pavement since the temperature of the top one to one and a quarter inch layer of asphalt which has been heated to a softened state is not sufficiently high enough when the heated asphalt is inserted into a full depth crack to form a homogeneous weld with the portions of the asphalt pavement surrounding the crack at the lower regions of the full depth crack. Due to the known practice in the industry of heating asphalt only to a temperature of 325.degree. F. to 350.degree. F. to prevent deterioration of the asphalt, such methods are incapable of repairing full depth thermal cracks or cold joints extending completely or substantially through six to eight inches of an asphalt pavement.
Thus, it would be desirable to provide a method for repairing cracks in asphaltic roads in which heated asphalt material inserted into the crack form a homogeneous weld with the surrounding asphalt material even where the crack extends the full depth or substantially through the full six to eight inches of the asphalt pavement. It would also be desirable to provide a method for repairing full depth cracks in asphaltic pavement which is simple in application.